1. Field of the Invention
This invention relates to millimeter-wave (MMW) circuit technology, and more particularly, to a miniaturized multilayer hybrid-phase signal splitter circuit whose signal processing function is fully equivalent to a conventional rat-race coupler, but having a specialized circuit layout structure that allows its IC implementation to be more miniaturized than the conventional rat-race coupler.
2. Description of Related Art
Rat-race couplers are also referred to as hybrid-phase ring couplers which are typically used as a circuit component in a millimeter-wave (MMW) mixer. In operation, the rat-race coupler receives the input of a carrier signal RF and the input of a local oscillation signal LO and splits the RF signal into a pair of in-phase output signals (i.e., phase difference is 0 degree) and also splits the LO signal into a pair of opposite-phase output signals (i.e., phase difference is 180 degrees) which can be used by the mixer circuit for generation of an intermediate frequency (IF) signal. The jargon “rat race” in the name of this device comes from the fact that its body structure includes a ring-shaped waveguide that looks like a circular cage used for rat race.
In structure, a rat-race coupler includes a ring-shaped 3/2-wavelength waveguide and four leg-like quarter-wavelength waveguides protruding from the ring-shaped waveguide. Since the structure and function of the rat-race coupler is well-known, detailed description thereof will not be given in this specification.
One drawback to the rat-race coupler, however, is that it has a relatively bulky size that makes it unsuitable for use in miniaturized integrated circuitry. Solutions to this problem include, for example, the following US patents:    (1) U.S. Pat. No. 7,068,122 “Miniatured multilayer balun”;    (2) U.S. Pat. No. 7,157,986 “Three-dimensional balun”;    (3) U.S. Pat. No. 5,634,208 “Multilayer transmission line hybrid”.
The U.S. Pat. No. 7,068,122 “Miniatured multilayer balun” discloses a multilayer architecture for construction of a balun with miniaturized size for integration to mixers. One drawback to this patent, however, is that it can only generate a pair of opposite-phase output signals and cannot provide a pair of in-phase output signals, and therefore cannot be used in place of the rat-race coupler.
The U.S. Pat. No. 7,157,986 “Three-dimensional balun” discloses a 3-dimensional architecture for balun construction. However, similar to the aforementioned patent, this patent can only generate a pair of opposite-phase output signals and cannot provide a pair of in-phase output signals, and therefore cannot be used in place of the rat-race coupler.
The U.S. Pat. No. 5,634,208 “Multilayer transmission line hybrid” discloses a multilayer architecture as an improvement on the conventional rat-race coupler. However, this improved rat-race coupler is nonetheless relatively bulky in size for miniaturized IC implementation.